Pulmonary edema is a feature of the acute phase of Adult Respiratory Distress Syndrome and may result from heart failure. Unfortunately, little work has been done to characterize the barriers to fluid transudation in normal lung and much less during periods when this transudation is increased. Specifically, the microvascular endothelial barrier and the alveolar epithelial barrier have not been investigated in detail. In addition, fluid transport through the interstitial space has not been well characterized. Goats with chronic lung lymph fistulae provide an animal model to investigate these parameters. This project is designed to determine: 1) The endothelial permeability surface area product (PS), its reflection coefficient (sigma), and its fluid filtration coefficient (Kf). (In the process of determining Kf it will be necessary to determine the pulmonary interstitial pressure). 2) The epithelial permeability-surface area product (PSA) and its reflection coefficient (sigma A). 3) Interstitial space mean transit time (t), distribution volume (Vd), and excluded volume (Ve). Distribution volume will be determined by multiplying the t by the flow across the microvascular barrier due to both diffusion and convection. Diffusion is found to be the dominant mechanism of transport for small molecules. The values of PS, sigma, Kf, PSA, sigma A, t, Vd and Ve, will be determined for a number of different molecular weight proteins that have a fluorescent label. This will be done for normal goats, goats with increased lung lymph flow due to increased pulmonary microvascular pressure and following infusions of histamine.